Human skin is tissue which is commonly treated in order to improve its visual appearance. Skin is composed of three basic elements: the epidermis, the dermis and the hypodermis or so called subcutis. The outer and also thinnest layer of skin is the epidermis. Epidermis contains mainly stratified squamous epithelium of which the outer side keratinizes and ensures coverage whereas the inner side contains a pigment. The dermis consists of collagen, elastic tissue and reticular fibers. The hypodermis is the lowest layer of the skin and contains hair follicle roots, lymphatic vessels, collagen tissue, nerves and also fat forming a subcutaneous white adipose tissue (SWAT).
SWAT is formed by aggregation of fat cells ranging up to 120 microns in diameter and containing as much as 95% glycerides and fatty acids by volume. Overeating and unhealthy lifestyles may result in an increase of size and/or number of the fat cells. The fat cells create lobules which are bounded by connective tissue, fibrous septa (retinaculum cutis).
Another part of adipose tissue is located in peritoneal cavity and is known as abdominal obesity. Visceral fat layer forming visceral white adipose tissue (VWAT) is located between parietal peritoneum and visceral peritoneum, closely below muscle fibers adjoining the hypodermis layer.
Excess of adipose tissue in subcutaneous or abdominal area may be perceived as aesthetically undesirable, mainly in the buttocks, thighs, abdomen or hips, where even weight loss after dieting and exercise may not lead to satisfactory results. Moreover, in the last few decades, more people suffer from growth of visceral white adipose tissue (VWAT) mainly in their abdominal area. Visceral fat has been also linked to various cardiovascular diseases and diabetes.
The undesirable topographic skin appearance may also be caused by changes in dermal or sub-dermal layer of the skin, especially by excessive number or volume of fat cells, weakening of fibrous septas, loss of elasticity and/or limited lymph flow, which may result in accumulation of toxins.
Mechanical stimulation includes acoustic, ultrasound and/or shock waves. Shock waves are waves characterized by steep pressure amplitude growth in comparison to the surrounding pressure. Despite their relationship with other types of mechanical stimulation, shock waves are different mainly in pressure magnitude and shape of the pressure wave. In comparison to ultrasound waves where the pressure periodically oscillates with limited bandwidth and amplitude, shock waves are characterized by non-linearity during the wave propagation. In the present invention, shock wave propagation is characterized by swift positive pressure increase in the range from one nanosecond up to 100 microseconds with positive peak pressure amplitudes up to 150 MPa. In comparison, regular ultrasound methods have positive peak pressure amplitudes up to about 3 MPa. The pulse duration (based on the time the pressure exceeds a half value of peak positive pressure) is preferably in the range of hundreds of nanoseconds to 10-100 of microseconds.
There are four main principles for generating shock waves: electrohydraulic, piezoelectric, electromagnetic and ballistic. The shock waves produced by electrohydraulic principle, piezoelectric principle or electromagnetic principle are traditionally used for destruction of calculi e.g. kidney stones. As these shock waves are focused, they may be characterized as hard shock waves because the energy is directed into small point in the tissue.
The ballistic shock waves have a naturally non-focused/radial propagation. Radial/non-focused propagation is characterized by smooth propagation.
Various non-invasive methods for skin treatment containing light, radiofrequency, microwave, and ultrasound treatment has been previously developed. Nevertheless, improved treatments in aesthetic medicine are needed.